Gut Microbiome in Non-Alcoholic Fatty Liver Disease: From Mechanisms to Therapeutic Role

Ling-Gui-Zhu-Gan decoction ameliorates nonalcoholic fatty liver disease via modulating the gut microbiota

Numerous studies have supported that nonalcoholic fatty liver disease (NAFLD) is highly associated with gut microbiota dysbiosis. Ling-Gui-Zhu-Gan decoction (LG) has been clinically used to treat NAFLD, but the underlying mechanism remains unknown. This study investigated the therapeutic effect and mechanisms of LG in mice with NAFLD induced by a high-fat diet (HD). An HD-induced NAFLD mice model was established to evaluate the efficacy of LG followed by biochemical and histopathological analysis. Metagenomics, metabolomics, and transcriptomics were used to explore the structure and metabolism of the gut microbiota. LG significantly improved hepatic function and decreased lipid droplet accumulation in HD-induced NAFLD mice. LG reversed the structure of the gut microbiota that is damaged by HD and improved intestinal barrier function. Meanwhile, the LG group showed a lower total blood bile acids (BAs) concentration, a shifted BAs composition, and a higher fecal short-chain fatty acids (SCFAs) concentration. Furthermore, LG could regulate the hepatic expression of genes associated with the primary BAs biosynthesis pathway and peroxisome proliferator-activated receptor (PPAR) signaling pathway. Our study suggested that LG could ameliorate NAFLD by altering the structure and metabolism of gut microbiota, while BAs and SCFAs are considered possible mediating substances.

IMPORTANCE

Until now, there has still been no study on the gut microbiota and metabolomics of Ling-Gui-Zhu-Gan decoction (LG) in nonalcoholic fatty liver disease (NAFLD) mouse models. Our study is the first to report on the reshaping of the structure and metabolism of the gut microbiota by LG, as well as explore the potential mechanism underlying the improvement of NAFLD. Specifically, our study demonstrates the potential of gut microbial-derived short-chain fatty acids (SCFAs) and blood bile acids (BAs) as mediators of LG therapy for NAFLD in animal models. Based on the results of transcriptomics, we further verified that LG attenuates NAFLD by restoring the metabolic disorder of BAs via the up-regulation of Fgf15/FXR in the ileum and down-regulation of CYP7A1/FXR in the liver. LG also reduces lipogenesis in NAFLD mice by mediating the peroxisome proliferator-activated receptor (PPAR) signaling pathway, which then contributes to reducing hepatic inflammation and improving intestinal barrier function to treat NAFLD.

Prebiotic Treatment in Patients with Nonalcoholic Fatty Liver Disease (NAFLD)-A Randomized Pilot Trial

Several studies show that gut microbiotas in patients with nonalcoholic fatty liver disease (NAFLD) differ from those in a healthy population, suggesting that this alteration plays a role in NAFLD pathogenesis. We investigated whether prebiotic administration affects liver fat content and/or liver-related and metabolic parameters. Patients with NAFLD and metabolic syndrome (age: 50 ± 11; 79% men) were randomized to receive either 16 g/day of prebiotic (ITFs-inulin-type fructans) (n = 8) or placebo (maltodextrin) (n = 11) for 12 weeks. Patients were instructed to maintain a stable weight throughout the study. Liver fat content (measured by H1MRS), fecal microbiota, and metabolic, inflammatory, and liver parameters were determined before and after intervention. Fecal samples from patients who received the prebiotic had an increased content of Bifidobacterium (p = 0.025), which was not observed with the placebo. However, the baseline and end-of-study liver fat contents did not change significantly in the prebiotic and placebo groups, neither did the liver function tests' metabolic and inflammatory mediators, including fibroblast growth factor-19 and lipopolysaccharide-binding protein. Body weight remained stable in both groups. These findings suggest that prebiotic treatment without weight reduction is insufficient to improve NAFLD.

Diet-Induced Gut Dysbiosis and Leaky Gut Syndrome

Chronic gut inflammation promotes the development of metabolic diseases such as obesity. There is growing evidence which suggests that dysbiosis in gut microbiota and metabolites disrupt the integrity of the intestinal barrier and significantly impact the level of inflammation in various tissues, including the liver and adipose tissues. Moreover, dietary sources are connected to the development of leaky gut syndrome through their interaction with the gut microbiota. This review examines the effects of these factors on intestinal microorganisms and the communication pathways between the gut-liver and gut-brain axis. The consumption of diets rich in fats and carbohydrates has been found to weaken the adherence of tight junction proteins in the gastrointestinal tract. Consequently, this allows endotoxins, such as lipopolysaccharides produced by detrimental bacteria, to permeate through portal veins, leading to metabolic endotoxemia and alterations in the gut microbiome composition with reduced production of metabolites, such as short-chain fatty acids. However, the precise correlation between gut microbiota and alternative sweeteners remains uncertain, necessitating further investigation. This study highlights the significance of exploring the impact of diet on gut microbiota and the underlying mechanisms in the gut-liver and gut-brain axis. Nevertheless, limited research on the gut-liver axis poses challenges in comprehending the intricate connections between diet and the gut-brain axis. This underscores the need for comprehensive studies to elucidate the intricate gut-brain mechanisms underlying intestinal health and microbiota.

Impact of Adherence to the Mediterranean Diet on Antioxidant Status and Metabolic Parameters in NAFLD Patients: A 24-Month Lifestyle Intervention Study

BACKGROUND

The Mediterranean Diet (MedDiet) is recognized as a healthy dietary pattern. Non-alcoholic fatty liver disease (NAFLD) is characterized by the excessive accumulation of fat in the liver.

OBJECTIVES

To assess the antioxidant status in erythrocytes, plasma, and peripheral blood mononuclear cells (PBMCs) of NAFLD patients following a 24-month lifestyle intervention based on the MedDiet. Adult patients (n = 40; aged 40-60 years) diagnosed with NAFLD by magnetic resonance imaging were divided into two groups based on their adherence to the MedDiet. Consumption was assessed using a validated 143-item semiquantitative Food Frequency Questionnaire. Anthropometrics, biochemistry parameters, intrahepatic fat contents (IFC), antioxidants, and inflammatory biomarkers were measured in plasma and erythrocytes before and after the intervention.

RESULTS

After the intervention, body mass index (BMI) and plasma levels of total cholesterol, low-density lipoprotein cholesterol (LDL-chol), triglycerides, malondialdehyde (MDA), and cytokeratin-18 (CK18) decreased, and high-density lipoprotein cholesterol (HDL-chol) increased. Participants with high adherence to MedDiet showed lower IFC, hepatic enzyme (AST, ALT, and GGT), glycemia, oxidase LDL (oxLDL) plasma levels, and erythrocyte MDA levels. Higher antioxidant activity (erythrocyte catalase-CAT, superoxide dismutase-SOD, glutathione peroxidase-GPx, glutathione reductase-GRd, and total glutathione-GSH as well as PBMCs-CAT gene expression) was observed in these patients, along with a reduction of PBMCs reactive oxygen species production and Toll-like receptor 4 (TLR4) expression. Inverse associations were observed between adherence to the MedDiet and BMI, glycemia, AST, IFC, and CK18 plasma levels and oxLDL, CAT, SOD, and GRd activities in erythrocytes. A significant linear regression was observed between adherence to the MedDiet and antioxidant score.

CONCLUSIONS

Adherence to the MedDiet is associated with improved plasma and PBMC antioxidant and inflammatory biomarker profiles and high antioxidant defences in erythrocytes.

Immunology of gut microbiome and liver in non-alcoholic fatty liver disease (NAFLD): mechanisms, bacteria, and novel therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Most important contributors to its development are diet and obesity. Gut microbiome's importance for immune system and inflammatory pathways more widely accepted as an important component in NAFLD and other liver diseases' pathogenesis. In this article we review potential mechanisms of microbiome alteration of local and systemic immune responses leading to NAFLD's development, and how can modulate them for the treatment. Our review mentions different immune system pathways and microorganisms regulating metabolism, liver inflammation and fibrosis. We specifically point out TLR-4 as a potential key immune pathway activated by bacterial lipopolysaccharides producing pro-inflammatory cytokines in NAFLD. Also, we discuss three endotoxin-producing strains (Enterobacter cloacae B29, Escherichia coli PY102, Klebsiella pneumoniae A7) that can promote NAFLD development via TLR4-dependent immune response activation in animal models and how they potentially contribute to disease progression in humans. Additionally, we discuss their other immune and non-immune mechanisms contributing to NAFLD pathogenesis. In the end we point out gut microbiome researches' future perspective in NAFLD as a potential new target for both diagnostic and treatment.

Gut microbiota-derived indole compounds attenuate metabolic dysfunction-associated steatotic liver disease by improving fat metabolism and inflammation

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease, and its prevalence has increased worldwide in recent years. Additionally, there is a close relationship between MASLD and gut microbiota-derived metabolites. However, the mechanisms of MASLD and its metabolites are still unclear. We demonstrated decreased indole-3-propionic acid (IPA) and indole-3-acetic acid (IAA) in the feces of patients with hepatic steatosis compared to healthy controls. Here, IPA and IAA administration ameliorated hepatic steatosis and inflammation in an animal model of WD-induced MASLD by suppressing the NF-κB signaling pathway through a reduction in endotoxin levels and inactivation of macrophages. Bifidobacterium bifidum metabolizes tryptophan to produce IAA, and B. bifidum effectively prevents hepatic steatosis and inflammation through the production of IAA. Our study demonstrates that IPA and IAA derived from the gut microbiota have novel preventive or therapeutic potential for MASLD treatment.

NASH/NAFLD-Related Hepatocellular Carcinoma: An Added Burden

Hepatocellular carcinoma (HCC) is the most frequently found primary malignancy of the liver, showing an accelerated upward trend over the past few years and exhibiting an increasing relationship with metabolic syndrome, obesity, dyslipidemia and type 2 diabetes mellitus. The connection between these risk factors and the occurrence of HCC is represented by the occurrence of non-alcoholic fatty liver disease (NAFLD) which later, based on genetic predisposition and various triggers (including the presence of chronic inflammation and changes in the intestinal microbiome), may evolve into HCC. HCC in many cases is diagnosed at an advanced stage and can be an incidental finding. We present such a scenario in the case of a 41-year-old male patient who had mild obesity and mixed dyslipidemia, no family or personal records of digestive pathologies and who recently developed a history of progressive fatigue, dyspepsia and mild upper abdominal discomfort initially thought to be linked to post-COVID syndrome, as the patient had COVID-19 pneumonia a month prior. The abdominal ultrasound revealed a mild hepatomegaly with bright liver aspect of the right lobe (diffuse steatosis), a large zone of focal steatosis (segments IV, III and II) and a left lobe tumoral mass, highly suggestive of malignancy. Point shear wave elastography at the right lobe ruled out an end-stage chronic liver disease. Additional laboratory investigations, imaging studies (magnetic resonance imaging) and histopathological examination of liver fragments confirmed a highly aggressive HCC, with poorly differentiation-G3, (T4, N 1M 0) and stage IVA, associated with nonalcoholic steatohepatitis (NASH). A sorafenib course of treatment was attempted, but the patient discontinued it due to severe side effects. The subsequent evolution was extremely unfavorable, with rapid degradation, a few episodes of upper digestive bleeding, hepatic insufficiency and mortality in a couple of months. Conclusions: Diagnosis of NASH-related HCC is either an accidental finding or is diagnosed at an advanced stage. In order to earn time for a proper treatment, it becomes important to diagnose it at an early stage, for which regular check-ups should be performed in groups having the risk factors related to it. Patients suffering from obesity and mixed dyslipidemia should undergo periodic abdominal ultrasound examinations. This should be emphasized even more in the cases showing NASH. Complaints of any kind post-COVID-19 should be dealt with keenly as little is yet known about its virulence and its long-term side effects.

Urbanization associates with restricted gut microbiome diversity and delayed maturation in infants

Alterations of the microbiome are linked to increasingly common diseases such as obesity, allergy, and inflammatory bowel disease. Post-industrial lifestyles are thought to contribute to the gut microbiome alterations that cause or aggravate these diseases. Comparing communities across the industrialization spectrum can reveal associations between gut microbiome alterations and lifestyle and health, and help pinpoint which specific aspect of the post-industrial lifestyle is linked to microbiome alterations. Here, we compare the gut microbiomes of 60 mother and infant pairs from rural and urban areas of Senegal over two time points. We find that urban mothers, who were more frequently overweight, had different gut microbiome compositions than rural mothers, showing an expansion of Lachnospiraceae and Enterobacter. Urban infants, on the other hand, showed a delayed gut microbiome maturation and a higher susceptibility to infectious diseases. Thus, we identify new microbiome features associated with industrialization, whose association with disease may be further investigated.

Fructooligosaccharides and galactooligosaccharides improve hepatic steatosis via gut microbiota-brain axis modulation

Studies have shown that gut dysbiosis is associated with the steatotic liver disease associated with metabolic dysfunction (MALSD) and its severity. This study evaluated the effects of two commercially available prebiotics fructooligosaccharides (FOS) and galactooligosaccharides(GOS) on hepatic adipogenesis, inflammation, and gut microbiota in high-fat diet-induced MALSD. The results indicated that FOS and GOS effectively reduced insulin resistance, hyperglycaemia, triglyceridemia, cholesterolaemia, and IL-1β serum levels. Moreover, FOS and GOS modulated the lipogenic (SREBP-1c, ACC, and FAS) and lipolytic (ATGL) signalling pathways, and reduced inflammatory markers such as p-NFκB-65, IL-6, iNOS, COX-2, TNF-α, IL-1β, and nitrotyrosine. FOS and GOS also enhanced the abundance of acetate producers' bacteria Bacteroides acidifaciens and Bacteroides dorei. FOS and GOS also induced positive POMC/GPR43 neurons at the arcuate nucleus, indicating hypothalamic signalling modulation. Our results suggest that FOS and GOS attenuated MALSD by reducing the hepatic lipogenic pathways and intestinal permeability through the gut microbiota-brain axis.

MicroRNA-29a Compromises Hepatic Adiposis and Gut Dysbiosis in High Fat Diet-Fed Mice via Downregulating Inflammation

SCOPE

miR-29a expression patterns influence numerous physiological phenomena. Of note, upregulation of miR-29a ameliorates high-fat diet (HFD)-induced liver dysfunctions in mice. However, the miR-29a effect on gut microbiome composition and HFD-induced gut microbiota changes during metabolic disturbances remains unclear. The study provides compelling evidence for the protective role of miR-29a in gut barrier dysfunction and steatohepatitis.

METHODS AND RESULTS

miR-29a overexpressed mice (miR-29aTg) are bred to characterize intestinal, serum biochemical, and fecal microbiota profiling features compared to wild-type mice (WT). Mice are fed an HFD for 8 months to induce steatohepatitis, and intestinal dysfunction is determined via histopathological analysis. miR-29aTg has better lipid metabolism capability that decreases total cholesterol and triglyceride levels in serum than WT of the same age. The study further demonstrates that miR-29aTg contributes to intestinal integrity by maintaining periodic acid Schiff positive cell numbers and diversity of fecal microorganisms. HFD-induced bacterial community disturbance and steatohepatitis result in more severe WT than miR-29aTg. Gut microorganism profiling reveals Lactobacillus, Ruminiclostridium_9, and Lachnoclostridium enrichment in miR-29aTg and significantly decreases interleukin-6 expression in the liver and intestinal tract.

CONCLUSION

This study provides new evidence that sheds light on the host genetic background of miR-29a, which protects against steatohepatitis and other intestinal disorders.

Membrane Vesicles of Toxigenic Clostridioides difficile Affect the Metabolism of Liver HepG2 Cells

Clostridioides difficile infection (CDI) appears to be associated with different liver diseases. C. difficile secretes membrane vesicles (MVs), which may be involved in the development of nonalcoholic fatty liver disease (NALFD) and drug-induced liver injury (DILI). In this study, we investigated the presence of C. difficile-derived MVs in patients with and without CDI, and analyzed their effects on pathways related to NAFLD and DILI in HepG2 cells. Fecal extracellular vesicles from CDI patients showed an increase of Clostridioides MVs. C. difficile-derived MVs that were internalized by HepG2 cells. Toxigenic C. difficile-derived MVs decreased mitochondrial membrane potential and increased intracellular ROS compared to non-toxigenic C. difficile-derived MVs. In addition, toxigenic C. difficile-derived MVs upregulated the expression of genes related to mitochondrial fission (FIS1 and DRP1), antioxidant status (GPX1), apoptosis (CASP3), glycolysis (HK2, PDK1, LDHA and PKM2) and β-oxidation (CPT1A), as well as anti- and pro-inflammatory genes (IL-6 and IL-10). However, non-toxigenic C. difficile-derived MVs did not produce changes in the expression of these genes, except for CPT1A, which was also increased. In conclusion, the metabolic and mitochondrial changes produced by MVs obtained from toxigenic C. difficile present in CDI feces are common pathophysiological features observed in the NAFLD spectrum and DILI.

Understanding NAFLD: From Case Identification to Interventions, Outcomes, and Future Perspectives

While non-alcoholic fatty liver disease (NAFLD) is a prevalent and frequent cause of liver-related morbidity and mortality, it is also strongly associated with cardiovascular disease-related morbidity and mortality, likely driven by its associations with insulin resistance and other manifestations of metabolic dysregulation. However, few satisfactory pharmacological treatments are available for NAFLD due in part to its complex pathophysiology, and challenges remain in stratifying individual patient's risk for liver and cardiovascular disease related outcomes. In this review, we describe the development and progression of NAFLD, including its pathophysiology and outcomes. We also describe different tools for identifying patients with NAFLD who are most at risk of liver-related and cardiovascular-related complications, as well as current and emerging treatment options, and future directions for research.

Modulatory effect of camel milk on intestinal microbiota of mice with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common metabolic disease of life, usually caused by unhealthy diet and lifestyle. Compared to normal individuals, the structure of the intestinal flora of NAFLD patients is altered accordingly. This study investigates the effect of camel milk on the regulation of intestinal flora structure in mice with high-fat diet-induced NAFLD. NAFLD model was established by feeding C57BL/6J mice a high-fat diet for 12 weeks, meanwhile camel milk (3.0 g/kg/d), cow milk (3.0 g/kg/d), and silymarin (200 mg/kg/d) were administered by gavage, respectively. Food intake and changes of physiological indexes in mice were observed and recorded. The 16S rRNA gene V3-V4 region was sequenced and the intestinal flora diversity and gene function were predicted in the colon contents of mice from different group. The results showed that camel milk enhanced glucolipid metabolism by downregulate the levels of blood glucose and triglyceride (TG) in serum, reduced lipid accumulation by downregulate the level of TG in the liver and improved liver tissue structure in NAFLD mice (p < 0.05). Meanwhile, camel milk had a positive modulatory effect on the intestinal flora of NAFLD mice, increasing the relative abundance of beneficial bacteria and decreasing the relative abundance of harmful bacteria in the intestinal flora of NAFLD mice, and silymarin had a similar modulatory effect. At the genus level, camel milk increased the relative abundance of Bacteroides, norank_f_Muribaculaceae and Alloprevotella and decreased the relative abundance of Dubosiella and Coriobacteriaceae_UCG-002 (p < 0.05). Camel milk also enhanced Carbohydrate metabolism, Amino acid metabolism, Energy metabolism, Metabolism of cofactors and vitamins and Lipid metabolism in NAFLD mice, thus reducing the degree of hepatic lipid accumulation in NAFLD mice and maintaining the normal structure of the liver. In conclusion, camel milk can improve the structure and diversity of intestinal flora and enhance the levels of substance and energy metabolism in NAFLD mice, which has a positive effect on alleviating NAFLD and improving the structure of intestinal flora.

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Age-Related NAFLD: The Use of Probiotics as a Supportive Therapeutic Intervention

Human aging, a natural process characterized by structural and physiological changes, leads to alterations of homeostatic mechanisms, decline of biological functions, and subsequently, the organism becomes vulnerable to external stress or damage. In fact, the elderly population is prone to develop diseases due to deterioration of physiological and biological systems. With aging, the production of reactive oxygen species (ROS) increases, and this causes lipid, protein, and DNA damage, leading to cellular dysfunction and altered cellular processes. Indeed, oxidative stress plays a key role in the pathogenesis of several chronic disorders, including hepatic diseases, such as non-alcoholic fatty liver disease (NAFLD). NAFLD, the most common liver disorder in the Western world, is characterized by intrahepatic lipid accumulation; is highly prevalent in the aging population; and is closely associated with obesity, insulin resistance, hypertension, and dyslipidemia. Among the risk factors involved in the pathogenesis of NAFLD, the dysbiotic gut microbiota plays an essential role, leading to low-grade chronic inflammation, oxidative stress, and production of various toxic metabolites. The intestinal microbiota is a dynamic ecosystem of microbes involved in the maintenance of physiological homeostasis; the alteration of its composition and function, during aging, is implicated in different liver diseases. Therefore, gut microbiota restoration might be a complementary approach for treating NAFLD. The administration of probiotics, which can relieve oxidative stress and elicit several anti-aging properties, could be a strategy to modify the composition and restore a healthy gut microbiota. Indeed, probiotics could represent a valid supplement to prevent and/or help treating some diseases, such as NAFLD, thus improving the already available pharmacological intervention. Moreover, in aging, intervention of prebiotics and fecal microbiota transplantation, as well as probiotics, will provide novel therapeutic approaches. However, the relevant research is limited, and several scientific research works need to be done in the near future to confirm their efficacy.

Diagnostic scores and scales for appraising Nonalcoholic fatty liver disease and omics perspectives for precision medicine

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) is a rising epidemic burden affecting around 25% of the global population. Liver biopsy remains the reference for NAFLD. However, the application of several scales and clinical algorithms have been proposed to diagnose NAFLD using prediction questions and blood biomarkers. This review presents a summarized of the currently available and emerging diagnostic biomarkers and scores used to assess NAFLD.

RECENT FINDINGS

The limitations of liver biopsy have fostered the development of alternative noninvasive strategies, which have been an area of intensive investigation over the past years. Diagnostic scores for NAFLD have shown to be a good alternative for disease diagnosis and prognosis due to a suitable applicability, good inter-laboratory reproducibility and widespread potential availability with reasonable costs.

SUMMARY

The growing NAFLD pandemic urges clinicians to seek alternatives for screening, early diagnosis, and follow-up, especially for those with contraindications for liver biopsy. New promising noninvasive biomarkers and techniques have been developed, evaluated and assessed, including diagnostic biomarkers scores. Moreover, multiomics markers panels involving phenotype, genotype, microbiome and clinical characteristics from patients will facilitate the diagnosis, stratification and prognosis of NAFLD patients with precision medicine approaches.